Mercedes' latest concept car is, in its own words, 'pure, rendered science fiction'. This is the new Ener-G-Force, a one-off model depicting a civilian version of a futuristic police car.

It's a product of the 2012 Los Angeles Design Challenge, which briefed manufacturers to dream up their vision for a highway patrol vehicle fit for the year 2025. Suspend your disbelief and read on for more Ener-G-Force details below...

So this is a model of a police-derived civilian car?

Yes, but it's not quite as confusing as that sounds. The original design proposal for the police version inspired Mercedes' American design arm to create a 'road-legal' spec car - the very concept you see in our pictures.

Mercedes claims it takes direct inspiration from the G-class, as seen in the bluff, three-window glasshouse, boxy wheelarches, and wing-top indicator signals. It's more of a Hollywood caricature than a sensible update of the iconic Gelandewagen, though...

Talk me through some of the Ener-G-Force's details

Being a pure design study, the Californian designers have allowed themselves a healthy dollop of poetic licence. Note the G-shaped LED headlight strips, and the 20-inch wheels with huge knobbly rubber. The roof-mounted lights recall now-defunct Hummer, and the G-wagen's rear-mounted spare wheel-carrier has been reimagined as a pull-out toolbox. Is Mercedes that worried about potential reliability?

Speaking of which, what powers the Ener-G-Force?

Nothing - it's only a model. However, Mercedes touts that a 2025 'production version' would be fuelled by recycled water stored in roof-mounted tanks. By transferring the water into an on-board 'hydro-tech converter' and converting it to hydrogen, the car's fuel-cell would generate electricity and store it in 'easily accessible side skirt units' which change colour through the charging process.

The on-board electric power station would give a hypothetical 800km (497-mile) range via the four wheel hub-mounted motors, and as a hydrogen fuel-cell party piece, emit nothing but water. There is, you see, a modicum of method among the madness.

In a small nod to common sense, the 'Terra-Scan' system, which uses a 360-degree topography scanner to adapt damping rates for surrounding conditions, isn't massively removed from the new automatic Terrain Response system fitted to the new Range Rover. Still, we'd expect future interpretations of the classic G-wagen to be a far more conventional affair than the design-directed Ener-G-Force.